org.apache.commons.collections.buffer
Class PriorityBuffer<E>

java.lang.Object
  java.util.AbstractCollection<E>
      org.apache.commons.collections.buffer.PriorityBuffer<E>

All Implemented Interfaces:

Iterable<E>, Collection<E>, Buffer<E>

public class PriorityBuffer<E>
extends AbstractCollection<E>
implements Buffer<E>

Binary heap implementation of Buffer that provides for removal based on Comparator ordering.

The removal order of a binary heap is based on either the natural sort order of its elements or a specified Comparator. The remove() method always returns the first element as determined by the sort order. (The ascendingOrder flag in the constructors can be used to reverse the sort order, in which case remove() will always remove the last element.) The removal order is not the same as the order of iteration; elements are returned by the iterator in no particular order.

The add(Object) and remove() operations perform in logarithmic time. The get() operation performs in constant time. All other operations perform in linear time or worse.

Note that this implementation is not synchronized. Use BufferUtils.synchronizedBuffer(Buffer) or SynchronizedBuffer.decorate(Buffer) to provide synchronized access to a PriorityBuffer:

 Buffer heap = SynchronizedBuffer.decorate(new PriorityBuffer());
 

Since:

Commons Collections 3.0 (previously BinaryHeap v1.0)

Version:

$Revision: 1.1.1.1 $ $Date: 2005/05/23 04:33:54 $

Author:

Peter Donald, Ram Chidambaram, Michael A. Smith, Paul Jack, Matt Hall, John Watkinson, Stephen Colebourne

Field Summary

protected boolean	ascendingOrder If true, the first element as determined by the sort order will be returned.
protected Comparator<? super E>	comparator The comparator used to order the elements
protected E[]	elements The elements in this buffer.
protected int	size The number of elements currently in this buffer.

Constructor Summary

PriorityBuffer()
Constructs a new empty buffer that sorts in ascending order by the natural order of the objects added.

PriorityBuffer(boolean ascendingOrder)
Constructs a new empty buffer specifying the sort order and using the natural order of the objects added.

PriorityBuffer(boolean ascendingOrder, Comparator<? super E> comparator)
Constructs a new empty buffer specifying the sort order and comparator.

PriorityBuffer(Comparator<? super E> comparator)
Constructs a new empty buffer that sorts in ascending order using the specified comparator.

PriorityBuffer(int capacity)
Constructs a new empty buffer that sorts in ascending order by the natural order of the objects added, specifying an initial capacity.

PriorityBuffer(int capacity, boolean ascendingOrder)
Constructs a new empty buffer that specifying initial capacity and sort order, using the natural order of the objects added.

PriorityBuffer(int capacity, boolean ascendingOrder, Comparator<? super E> comparator)
Constructs a new empty buffer that specifying initial capacity, sort order and comparator.

PriorityBuffer(int capacity, Comparator<? super E> comparator)
Constructs a new empty buffer that sorts in ascending order using the specified comparator and initial capacity.

Method Summary

boolean	add(E element) Adds an element to the buffer.
void	clear() Clears all elements from the buffer.
Comparator<? super E>	comparator() Gets the comparator being used for this buffer, null is natural order.
protected int	compare(E a, E b) Compares two objects using the comparator if specified, or the natural order otherwise.
E	get() Gets the next element to be removed without actually removing it (peek).
protected void	grow() Increases the size of the heap to support additional elements
boolean	isAscendingOrder() Checks whether the heap is ascending or descending order.
protected boolean	isAtCapacity() Tests if the buffer is at capacity.
Iterator<E>	iterator() Returns an iterator over this heap's elements.
protected void	percolateDownMaxHeap(int index) Percolates element down heap from the position given by the index.
protected void	percolateDownMinHeap(int index) Percolates element down heap from the position given by the index.
protected void	percolateUpMaxHeap(E element) Percolates a new element up heap from the bottom.
protected void	percolateUpMaxHeap(int index) Percolates element up heap from from the position given by the index.
protected void	percolateUpMinHeap(E element) Percolates a new element up heap from the bottom.
protected void	percolateUpMinHeap(int index) Percolates element up heap from the position given by the index.
E	remove() Gets and removes the next element (pop).
int	size() Returns the number of elements in this buffer.
String	toString() Returns a string representation of this heap.

Methods inherited from class java.util.AbstractCollection

addAll, contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toArray

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

addAll, contains, containsAll, equals, hashCode, isEmpty, remove, removeAll, retainAll, toArray, toArray

Field Detail

elements

protected E[] elements

The elements in this buffer.

size

protected int size

The number of elements currently in this buffer.

ascendingOrder

protected boolean ascendingOrder

If true, the first element as determined by the sort order will be returned. If false, the last element as determined by the sort order will be returned.

comparator

protected Comparator<? super E> comparator

The comparator used to order the elements

Constructor Detail

PriorityBuffer

public PriorityBuffer()

Constructs a new empty buffer that sorts in ascending order by the natural order of the objects added.

PriorityBuffer

public PriorityBuffer(Comparator<? super E> comparator)

Constructs a new empty buffer that sorts in ascending order using the specified comparator.

Parameters:

comparator - the comparator used to order the elements, null means use natural order

PriorityBuffer

public PriorityBuffer(boolean ascendingOrder)

Constructs a new empty buffer specifying the sort order and using the natural order of the objects added.

Parameters:

ascendingOrder - if true the heap is created as a minimum heap; otherwise, the heap is created as a maximum heap

PriorityBuffer

public PriorityBuffer(boolean ascendingOrder,
                      Comparator<? super E> comparator)

Constructs a new empty buffer specifying the sort order and comparator.

Parameters:

ascendingOrder - true to use the order imposed by the given comparator; false to reverse that order

comparator - the comparator used to order the elements, null means use natural order

PriorityBuffer

public PriorityBuffer(int capacity)

Constructs a new empty buffer that sorts in ascending order by the natural order of the objects added, specifying an initial capacity.

Parameters:

capacity - the initial capacity for the buffer, greater than zero

Throws:

IllegalArgumentException - if capacity is <= 0

PriorityBuffer

public PriorityBuffer(int capacity,
                      Comparator<? super E> comparator)

Constructs a new empty buffer that sorts in ascending order using the specified comparator and initial capacity.

Parameters:

capacity - the initial capacity for the buffer, greater than zero

comparator - the comparator used to order the elements, null means use natural order

Throws:

IllegalArgumentException - if capacity is <= 0

PriorityBuffer

public PriorityBuffer(int capacity,
                      boolean ascendingOrder)

Constructs a new empty buffer that specifying initial capacity and sort order, using the natural order of the objects added.

Parameters:

capacity - the initial capacity for the buffer, greater than zero

ascendingOrder - if true the heap is created as a minimum heap; otherwise, the heap is created as a maximum heap.

Throws:

IllegalArgumentException - if capacity is <= 0

PriorityBuffer

public PriorityBuffer(int capacity,
                      boolean ascendingOrder,
                      Comparator<? super E> comparator)

Constructs a new empty buffer that specifying initial capacity, sort order and comparator.

Parameters:

capacity - the initial capacity for the buffer, greater than zero

ascendingOrder - true to use the order imposed by the given comparator; false to reverse that order

comparator - the comparator used to order the elements, null means use natural order

Throws:

IllegalArgumentException - if capacity is <= 0

Method Detail

isAscendingOrder

public boolean isAscendingOrder()

Checks whether the heap is ascending or descending order.

Returns:

true if ascending order (a min heap)

comparator

public Comparator<? super E> comparator()

Gets the comparator being used for this buffer, null is natural order.

Returns:

the comparator in use, null is natural order

size

public int size()

Returns the number of elements in this buffer.

Specified by:

size in interface Collection<E>

Specified by:

size in class AbstractCollection<E>

Returns:

the number of elements in this buffer

clear

public void clear()

Clears all elements from the buffer.

Specified by:

clear in interface Collection<E>

Overrides:

clear in class AbstractCollection<E>

add

public boolean add(E element)

Adds an element to the buffer.

The element added will be sorted according to the comparator in use.

Specified by:

add in interface Collection<E>

Overrides:

add in class AbstractCollection<E>

Parameters:

element - the element to be added

Returns:

true always

get

public E get()

Gets the next element to be removed without actually removing it (peek).

Specified by:

get in interface Buffer<E>

Returns:

the next element

Throws:

BufferUnderflowException - if the buffer is empty

remove

public E remove()

Gets and removes the next element (pop).

Specified by:

remove in interface Buffer<E>

Returns:

the next element

Throws:

BufferUnderflowException - if the buffer is empty

isAtCapacity

protected boolean isAtCapacity()

Tests if the buffer is at capacity.

Returns:

true if buffer is full; false otherwise.

percolateDownMinHeap

protected void percolateDownMinHeap(int index)

Percolates element down heap from the position given by the index.

Assumes it is a minimum heap.

Parameters:

index - the index for the element

percolateDownMaxHeap

protected void percolateDownMaxHeap(int index)

Percolates element down heap from the position given by the index.

Assumes it is a maximum heap.

Parameters:

index - the index of the element

percolateUpMinHeap

protected void percolateUpMinHeap(int index)

Percolates element up heap from the position given by the index.

Assumes it is a minimum heap.

Parameters:

index - the index of the element to be percolated up

percolateUpMinHeap

protected void percolateUpMinHeap(E element)

Percolates a new element up heap from the bottom.

Assumes it is a minimum heap.

Parameters:

element - the element

percolateUpMaxHeap

protected void percolateUpMaxHeap(int index)

Percolates element up heap from from the position given by the index.

Assume it is a maximum heap.

Parameters:

index - the index of the element to be percolated up

percolateUpMaxHeap

protected void percolateUpMaxHeap(E element)

Percolates a new element up heap from the bottom.

Assume it is a maximum heap.

Parameters:

element - the element

compare

protected int compare(E a,
                      E b)

Compares two objects using the comparator if specified, or the natural order otherwise.

Parameters:

a - the first object

b - the second object

Returns:

-ve if a less than b, 0 if they are equal, +ve if a greater than b

grow

protected void grow()

Increases the size of the heap to support additional elements

iterator

public Iterator<E> iterator()

Returns an iterator over this heap's elements.

Specified by:

iterator in interface Iterable<E>

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in class AbstractCollection<E>

Returns:

an iterator over this heap's elements

toString

public String toString()

Returns a string representation of this heap. The returned string is similar to those produced by standard JDK collections.

Overrides:

toString in class AbstractCollection<E>

Returns:

a string representation of this heap